Rain. for a very considerable time. Neither can we admit the winds to have any considerable agency in this matter, since we find that blowing upon vapour is so far from condensing it, that it unites it more closely with the air, and wind is found to be a great promoter of evaporation. According to Robault, the great cause of rain is the heat of the air; which, after continuing for some time near the earth, is raised on high by a wind, and there thawing the snowy villi or flocks of half-frozen vesiculæ, reduces them to drops; which, coalescing, descend. Here, however, we ought to be informed by what means these vesiculæ are suspended in their halffrozen state; since the thawing of them can make but little difference in their specific gravity, and it is certain that they ascended through the air not in a frozen but in an aqueous state. Dr Clarke and others ascribe this descent of the rain rather to an alteration of the atmosphere than of the vesicula; and suppose it to arise from a diminution of the elastic force of the air. This elasticity, which, they say, depends chiefly or wholly upon terrene exhalations, being weakened, the atmosphere sinks under its burden, and the clouds fall. Now, the little vesicles being once upon the descent, will continue therein, notwithstanding the increase of resistance they every moment meet with. For, as they all tend to the centre of the earth, the farther they fall, the more coalitions they will make; and the more coalitions, the more matter will there be under the same surface; the surface increasing only as the squares, but the solidity as the cubes; and the more matter under the same surface, the less resistance will there be to the same matter. Thus, if the cold, wind, &c. act early enough to precipitate the ascending vesicles before they are arrived at any considerable height, the coalitions being but few, the drops will be proportionably small; and thus is formed a dew. If the vapours be more copious, and rise a little higher, we have a mist or fog. A little higher still, and they produce a small rain; if they neither meet with cold nor wind, they form a heavy thick dark sky. This hypothesis is equally unsatisfactory with the others; for, granting that the descent and condensation of the vapours are owing to a diminution of the atmosphere's elasticity, by what is this diminution occasioned? To say that it is owing to terrene exhalations, is only solving one difficulty by another; since we are totally unacquainted both with the nature and operation of these exhalations. Besides, let us suppose the cause to be what it will, if it acts equally and at once upon all the vapour in the air, then all that vapour must be precipitated at once; and thus, instead of gentle showers continuing for a considerable length of time, we should have the most violent waterspouts, continuing only for a few minutes, or perhaps seconds, which, instead of refreshing the earth, would drown and lay waste every thing before them. Since philosophers have admitted the electric fluid to such a large share in the operations of nature, almost all the natural phenomena have been accounted for by the action of that fluid; and rain, among others, has been reckoned an effect of electricity. But this word, unless it be explained, makes us no wiser than we were before; the phenomena of artificial electricity having been explained on principles which could scarce apply in any degree to the electricity of nature: and Bain therefore all the solution we can obtain of the natural appearances of which we speak, comes to this, that rain is occasioned by a moderate electrification, hail and snow by one more violent, and thunder by the most violent of all; but in what manner this electrification is occasioned, has not yet been explained. The principles of electricity necessary to be attended to in the solution of the phenomena under consideration are the following: 1. The electric fluid and solar light are the same substances in two different modifications. 2. Electricity is the motion of the fluid when running, or attempting to run, in a continued stream from one place to another heat is when the fluid has no tendency but to vibrate outwards and inwards to and from a centre; or at least when its streams converge to a point or focus. 3. The fluid acting as electricity, like water, or any other fluid, always tends to the place where there is least resistance. On these three principles may the phenomena of atmospherical electricity, and the descent of rain by its means, he explained as follows: 1. The light or heat of the sun, acting in that pa culiar manner which we call heat, unites itself with the moisture of the earth, and forms it into vapour, which thus becomes specifically lighter than air, and of consequence ascends in the atmosphere to a certain height. 2. Besides the quantity of light which is thus united to the water, and forms it into vapour, a very considerable quantity enters the earth, where it assumes the nature of electric fluid. 3. As the earth is always full of that fluid, every quantity which enters must displace an equal quantity which is already there. 4. This quantity which is displaced must escape either at a distance from the place where the other en ters, or very near it. 5. At whatever place a quantity of electric matter escapes, it must electrify the air above that place where it has escaped; and as a considerable quantity of light must always be reflected from the earth into the atmosphere, where it does not combine with the aqueous vapour, we have thence another source of electricity to the air: as this quantity must undoubt edly assume the action of electric fluid, especially after the action of the sun has ceased. Hence the rea son why in serene weather the atmospherical electricity is always strongest, and rather more so in the night than in the day. 6. From these considerations, we see an evident rea son why there must commonly be a difference between the electricity of the earth and that of the atmosphere, excepting when an earthquake is about to ensue. The consequence of this must be, that as the action of the solar light continues to bring down the electric matter, and the earth continues to discharge an equal quantity of it into the atmosphere, some part of the atmosphere must at last become overloaded with it, and attempt to throw it back into the earth. This attempt will be vain, until a vent is found for the electricity at some other place; and as soon as this happens, the electrified atmosphere begins to throw off its superfluous electricity, and the earth to receive it. As the atmosphere itself Rain. is a bad conductor, and the more so the drier it is, the electric matter attacks the small aqueous particles which are detained in it by means of the latent heat. These being unable to bear the impetus of the fluid, throw out their latent heat, which easily escapes, and thus makes a kind of vacuum in the electrified part of the atmosphere. The consequences of this are, that the aqueous particles being driven together in large quantity, at last become visible, and the sky is covered with clouds; at the same time a wind blows against these clouds, and, if there is no resistance in the atmosphere, will drive them away. 7. But if the atmosphere all round the cloud is exceedingly electrified, and the earth is in no condition to receive the superfluous fluid excepting in that place which is directly under the cloud, then the whole electricity of the atmosphere for a vast way round will tend to that part only, and the cloud will be electrified to an extreme degree. A wind will now blow against the cloud from all quarters, more and more of the vapour will be extricated from the air by the electric matter, and the cloud will become darker and thicker, at the same time that it is in a manner stationary, as being acted upon by opposite winds; though its size is enlarged with great rapidity by the continual supplies of vapour brought by the winds. 8. The vapours which were formerly suspended invisibly by means of the latent heat are now suspended visibly by the electric fluid, which will not let them fall to the earth, until it is in a condition to receive the electric matter descending with the rain.It is easy to see, however, that thus every thing is prepared for a violent storm of thunder and lightning as well as rain. The surface of the earth becomes electrified from the atmosphere: but when this has continued for some time, a zone of earth considerably below the surface acquires an electricity opposite to that of the clouds and atmosphere; of consequence the electricity in the cloud being violently pressed on all sides, will at last burst out towards that zone where the resistance is least, as explained under the article LIGHTNING. The vapours now having lost that which supported them, will fall down in rain, if there is not a sufficient quantity of electric matter to keep them in the same state in which they were before: but if this happens to be the case, the cloud will instantly be charged again, while little or no rain will fall; and hence violent thunder sometimes takes place without any rain at all, or such as is quite inconsiderable in quantity. very 9. When the electricity is less violent, the rain will descend in vast quantity, especially after every flash of lightning; and great quantities of electric matter will thus be conveyed to the earth, insomuch that sometimes the drops have been observed to shine as if they were on fire, which has given occasion to the reports of fery rain having fallen on certain occasions. If the quantity of electric matter is smaller, so that the rain can convey it all gradually to the ground, there will be rain without any thunder; and the greater the quantity of electricity the more violent will be the rain. From this account of the causes of rain, we may see the reason why in warm climates the rains are excessive, and for the most part accompanied with thunder; for there the electricity of the atmosphere is immensely 4. greater than it is with us. We may also see why in certain places, according to the situation of mountains, seas, &c. the rains will be greater than in others, and likewise why some parts of the world are exempt ed from rain altogether; but as a particular discussion of these would necessarily include an explanation of the causes and phenomena of THUNDER, we shall for this reason refer the whole to be treated of under that article. Whether this theory be just, however, it would be too assuming in us to say. It may admit of dispute; for we must grant that in the very best systems, though an oocurrence so frequent, the theory of rain is but very im perfectly understood. Dr Hutton, whose speculations are always ingenious, though generally extraordinary, and much out of the common way, has given a new theory of rain in the first volume of the Transactions of the Royal Society of Edinburgh. It is well known that atmospheric air is capable of dissolving, with a certain degree of heat, a given quantity of water. The Doctor ascertains the ratio of the dissolving power of air, in relation to water, in different degrees of heat; and shows, that by mixing a portion of transparent humid warm air with a portion of cold air, the mixture becomes opaque, and part of the water will be precipitated; or, in other words, the vapour will be condensed into rain. The ratio which he states, however, does not appear to us to be supported by experience. Whether the electricity of the air changes in consequence of its depositing the water dissolved in it, or the change is a cause of this deposition, must remain uncertain; but, in either view, there must be an agent different from heat and cold, since the changes in these respects do not in other operations change the state of electricity. Dr Hutton supposes that heat and solution do not increase by equal increments; but that, in reality, if heat be supposed to increase by equal increments along a straight line, solution will be expressed by ordinates to a curve whose convex side is turned towards that line. That the power of solution is not increased in the same ratio with heat, is, however, hypothetical, except when we rise pretty high in the scale, when its proportional increase is a little doubtful; and it is not, in this paper, supported by experiment. The condensation of the breath in air is not an observation in point, except in air already saturated with vapour. It can amount, in any view, to no more than this, that to render it visible, the heat must be diminished in a greater proportion than can be compensated by the power of solution in the body of air, in which the portion expired is at first immersed. To explain rain from this cause, we must always suppose a constant diminution of heat to take place at the moment of the condensation of the vapour; but we actu ally find that the change from a state of vapour to the fluid state is attended with heat; so that rain must at once oppose its own cause, and continued rains would be impossible, without calling in the aid of other causes. From his own system, Dr Hutton endeavours to explain the regular and irregular seasons of rain, either respecting the generality of its appearance, or the regularity of its return. And to obviate the apparent exceptions of the theory, from the generality of rain, he explains the proportional quantities of rain, and adds a comparative estimate of climates, in relation to rain, with the meteorological observations made in our own climate.. Rain. Rain. As to the general quantity of rain that falls, and its Rain proportion in several places at the same time, and in the same place at several times, we have many observations, journals, &c. in the Memoirs of the French Academy, the Philosophical Transactions, &c. Upon measuring, then, the rain falling yearly, its depth, at a medium, and its proportion in several places, is found as in the following table: climate. As his principle is at least insufficient, and we think erroneous, it would be useless, even were this a proper place for it, to pursue these various branches, which must partake of the errors of the system. In these branches we ought to observe, that there are several just observations, mixed with errors, because evaporation and condensation must at last be the great basis of every theory: the mistakes arise from not being aware of all the causes, and misrepresenting the operation of those which do exist. In a work entitled Thoughts on Meteorology, vol. ii. M. de Luc considers very particularly the grand phenomenon of rain, and the numerous circumstances connected with it. He examines the several hypotheses with considerable care; but thinks them, even if admissible, utterly insufficient to account for the formation of rain. The grand question in this inquiry is, what becomes of the water that rises in vapour into the atmosphere; or what state it subsists in there, between the time of its evaporation and its falling down again in rain. If it continues in the state of watery vapour, or such as is the immediate product of evaporation, it must possess the distinctive characters essential to that fluid: it must make the hygrometer move towards humidity, in proportion as the vapour is more or less abundant in the air: on a diminution of heat, the humidity, as shown by the bygrometer, must increase; and on an increase of the heat the humidity must diminish; and the introduction of other hygroscopic substances, drier than the air, must have the same effect as an augmentation of heat. These are the properties of watery vapour, on every hypothesis of evaporation; and therefore all the water that exists in the atmosphere without possessing these properties, is no longer vapour, but must have changed its nature. M. de Luc shows, that the water which forms rain, though it has ever been considered and reasoned upon as producing humidity, does not possess these properties, and must therefore have passed into another state. As he thinks that the vapour passes into an invisible state in the interval between evaporation and its falling again in rain, and that in that state it is not sensible to the bygrometer, he considers the laws of hygrology as insufficient for explaining the formation of rain; but he does not pretend to have discovered the immediate cause of the formation of clouds and rain. If it is not in the immediate product of evaporation that rain has its source; if the vapours change their nature in the atmosphere, so as no longer to be sensible to the hygrometer, or to the eye; if they do not become vapour again till clouds appear; and if, when the clouds are formed, no alteration is perceived in the quality of the air-we must acknowledge it to be very probable, that the intermediate state of vapour is no other than air-and that the clouds do not proceed from any distinct fluid contained in the atmosphere, but from a decomposition of a part of the air itself, perfectly similar to the rest. It appears, to us at least, that M. de Luc's mode of reasoning on this subject agrees better with the phenomena than Dr Hutton's. The Doctor, however, thinks differently, and published answers to the objections of M. de Luc with regard to his theory of rain; to which M. de Luc replied in a letter which was printed in the Appendix to the 81st volume of the Monthly Review: but it would extend our article beyond its due bounds, to give a view of this controversy. At Townley, in Lancashire, observed by Mr Inches. Upminster, in Essex, by Mr Derham At Upminster. 1700 19 Inch. .03 1701 18 At Paris. 21 Inch..37 .69 42 194 321 434 19 24 ain. stens and softens the earth, and thus fits it for affording nourishment to plants; by falling on high mountains, it carries down with it many particles of loose earth, which serve to fertilize the surrounding valleys, and purifies the air from noxious exhalations, which tend in their return to the earth to meliorate the soil; it moderates the heat of the air; and is one means of supplying fountains and rivers. However, vehement rains in many countries are found to be attended with barrenness and poorness of the lands, and miscarriage of the crops in the succeeding year: and the reason is plain; for these excessive storms wash away the fine mould into the riverɛ, which carry it into the sea, and it is a long time before the land recovers itself again. The remedy to the famine, which some countries are subject to from this sort of mischief, is the planting large orchards and groves of such trees as bear esculent fruit; for it is an old observation, that in years, when grain succeeds worst, these trees produce most fruit of all. It may partly be owing to the thorough moistening of the earth, as deep as their roots go by these rains, and partly to their trunks stopping part of the light mould carried down by the rains, and by this means furnishing themselves with a coat of new earth. Preternatural RAINS. We have numerous accounts, in the historians of our own as well as other countries, of preternatural rains; such as the raining of stones, of dust, of blood, nay, and of living animals, as young frogs, and the like. We are not to doubt the truth of what those who are authors of veracity and credit relate to us of this kind, so far as to suppose that the falling of stones and dust never happened; the whole mistake is, the supposing them to have fallen from the clouds: but as to the blood and frogs, it is very certain that they never fell at all, but the opinion has been a mere decoption of the eyes. Men are extremely fond of the marvellous in their relations; but the judicious reader is to examine strictly whatever is reported of this kind, and is not to suffer himself to be deceived. There are two natural methods by which quantities of stones and dust may fall in certain places, without their having been generated in the clouds or fallen as rain. The one is by means of hurricanes: the wind which we frequently see tearing off the tiles of houses, and carrying them to considerable distances, being equal ly able to take up a quantity of stones, and drop them again at some other place. But the other, which is much the most powerful, and probably the most usual way, is for the eruptions of volcanoes and burning mountains to toss up, as they frequently do, a vast quantity of stones, ashes, and cinders, to an immense height in the air and these, being hurried away by the hurricanes and impetuous winds which usually accompany those eruptions, and being in themselves much lighter than common stones, as being half calcined, may easily be thus carried to vast distances; and there falling in places where the inhabitants know nothing of the occasion, they cannot but be supposed by the vulgar to fall on them from the clouds. It is well known, that, in the great eruptions of Ætna and Vesuvius, showers of ashes, dust, and small cinders, have been seen to obscure the air, and overspread the surface of the sea for a great way, and cover the decks of ships; and this at such a distance, as it should appear scarce conceivable that they should have been carried to: and probably, if the ac 3. counts of all the showers of these substances mentioned by authors be collected, they will all be found to have fallen within such distances of volcanoes; and if compared as to the time of their falling, will be found to correspond in that also with the eruptions of those mountains. We have known instances of the ashes from Vesuvius having been carried thirty, nay, forty leagues, and peculiar accidents may have carried them yet farther. It is not to be supposed that these showers of stones and dust fall for a continuance in the manner of showers of rain, or that the fragments or pieces are as frequent as drops of water; it is sufficient that a number of stones, or a quantity of dust, fall at once on a place, where the inhabitants can have no knowledge of the part from whence they came, and the vulgar will not doubt their dropping from the clouds. Nay, in the canton of Berne in Swisserland, the inhabitants accounted it a miracle that it rained earth and sulphur up. pon them at a time that a small volcano terrified them; and even while the wind was so boisterous, and hurricanes so frequent, that they saw almost every moment the dust, sand, and little stones torn up from the surface of the earth in whirlwinds, and carried to a considerable height in the air, they never considered that both the sulphur thrown up by the volcano, and the dust, &c. carried from their feet must fall soon after somewhere. It is very certain that in some of the terrible storms of large hail, where the hailstones have been of many inches round, on breaking them there have been found what people have called stones in their middle; but these observers needed only to have waited the dissolving of one of these hailstones, to have seen the stone in its centre disunite also, it being only formed of the particles of loose earthy matter, which the water exhaled, by the sun's heat, had taken up in extremely small moleculæ with it; and this only having served to give an opaque hue to the inner part of the congelation, to which the freezing of the water alone gave the apparent hardness of stone. The raining of blood has been ever accounted a more terrible sight and more fatal omen than the other preternatural rains already mentioned. It is very certain that nature forms blood nowhere but in the vessels of animals; and therefore showers of it from the clouds are by no means to be credited. Those who suppose that what has been taken for blood has been actually seen falling through the air, have had recourse to flying insects for its origin, and suppose it the eggs or dung of certain butterflies discharged from them as they were high up in the air. But it seems a very wild conjecture, as we know of no butterfly whose excrements or eggs are of such a colour, or whose abode is so high, or their flocks so numerous, as to be the occasion of this. It is most probable that these bloody waters were never seen falling; but that people seeing the standing waters blood-coloured, were assured, from their not knowing how it should else happen, that it had rained blood into them. A very memorable instance of this took place at the Hague in the year 1670. Swammerdam, who relates it, tells us, that one morning the whole town was in an uproar on finding their lakes and ditches full of blood, as they thought: and having been certainly full of water the night before, they agreed it must have rained blood in the night: but a certain phy sician Rain. Rain. soft-bodied animals: and they cannot be at this time Bain hatched immediately out of eggs; because the young frog does not make its appearance from the egg in form, but has its hinder legs enveloped in a skin, and is what we call a tadpole; and the young frogs are at least 100 times larger at the time of their appearance, than the egg from which they should be hatched. sician went down to one of the canals, and taking home a quantity of this blood-coloured water, he examined it by the microscope, and found that the water was water still, and had not at all changed its colour; but that it was full of prodigious swarms of small red animals, all alive, and very nimble in their motions, whose colour and prodigious number gave a red tinge to the whole body of the water they lived in, on a less accurate inspection. The certainty that this was the case, did not however persuade the Hollanders to part with the miracle: they prudently concluded, that the sudden appearance of such a number of animals was as great a prodigy as the raining of blood would have been; and are assured to this day, that this portent foretold the scene of war and destruction which Louis XIV. afterwards brought into that country, which had before enjoyed 40 years of uninterrupted peace. The animals which thus colour the water of lakes and ponds are the pulices arborescentes of Swammerdam, or the water-fleas with branched horns. These creatures are of a reddish-yellow or flame colour: they live about the sides of ditches, under weeds, and among the mud; and are therefore the less visible, except at a certain time, which is in the end or beginning of June: it is at this time that these little animals leave their recesses to float loose about the water, to meet for the propagation of their species, and by that means become visible in the colour they give the water. This is visible, more or less, in one part or other of almost all standing waters at this season; and it is always at this season that the bloody waters have alarmed the ignorant. The raining of frogs is a thing not less wonderful in the accounts of authors who love the marvellous, than those of blood or stones; and this is supposed to happen so often, that there are multitudes who pretend to have been eye-witnesses of it. These rains of frogs always happen after very dry seasons, and are much more frequent in the hotter countries than in the cold ones. In Italy they are very frequent; and it is not uncommon to see the streets of Rome swarming both with young frogs and toads in an instant in a shower of rain; they hopping everywhere between the people's legs as they walk, though there was not the least appearance of them before. Nay, they have been seen to fall through the air down upon the pavements. This seems a strong circumstance in favour of their being rained down from the clouds; but, when strictly examined, it comes to nothing for these frogs that are seen to fall, are always found dead, lamed, or bruised by the fall, and never hop about as the rest; and they are never seen to fall, except close under the walls of houses, from the roofs and gutters of which they have accidentally slipped down. Some people, who love to add to strange things yet stranger, affirm that they have had the young frogs fall into their hats in the midst of an open field; but this is idle, and wholly false. Others, who cannot agree to their falling from the clouds, have tried to solve the difficulty of their sudden appearance, by supposing them hatched out of the egg, or spawn, by these rains. Nay, some have supposed them made immediately out of the dust: but there are unanswerable arguments against all these suppositions. Equivocal generation, or the spontaneous production of animals out of dust, is now wholly exploded. The fall from the clouds must destroy and kill these tender and It is beyond a doubt, that the frogs which make their appearance at this time, were hatched and in being long before but that the dry seasons had injured them, and kept them sluggishly in holes or coverts; and that all the rain does, is the enlivening them, giving them new spirits, and calling them forth to seek new habitations, and enjoy the element they were destined in great part to live in. Theophrastus, the greatest of all the natu ralists of antiquity, has affirmed the same thing. We find that the error of supposing these creatures to fall from the clouds was as early as that author's time; and also that the truth, in regard to their appearance, was as early known; though, in the ages since, authors have taken care to conceal the truth, and to hand down to us the error. We find this venerable sage, in a fragment of his on the generation of animals which appear on a sudden, bantering the opinion, and asserting that they were hatched and living long before. The world owes, however, to the accurate Signior Redi the great proof of this truth, which Theophrastus only has affirmed: for this gentleman, dissecting some of these new-appearing frogs, found in their stomachs herbs and other halfdigested food; and, openly showing this to his credulous countrymen, asked them whether they thought that nature, which engendered, according to their opinion, these animals in the clouds, had also been so provident as to engender grass there for their food and nourishment? To the raining of frogs we ought to add the raining of grasshoppers and locusts, which have sometimes ap peared in prodigious numbers, and devoured the fruits of the earth. There has not been the least pretence for the supposing that these animals descended from the clouds, but that they appeared on a sudden in prodigi ous numbers. The naturalist, who knows the many accidents attending the eggs of these and other the like animals, cannot but know that some seasons will prove particularly favourable to the hatching them, and the prodigious number of eggs that many insects lay could not but every year bring us such abundance of the young, were they not liable to many accidents, and had not provident nature taken care, as in many plants, to continue the species by a very numerous stock of seeds, of which perhaps not one in 500 need take root in order to continue an equal number of plants. As it is thus also in regard to insects, it cannot but happen, that if a favourable season encourage the hatching of all those eggs, a very small number of which alone was necessary to continue the species, we must, in such seasons, have a proportionate abundance of them. There appeared about 50 years ago, in London, such a prodigious swarm of the little beetle called the lady-cow, that the very posts in the streets were everywhere covered with them. But thanks to the progress of philosophy among us, we had nobody to assert that it rained cow-ladies, but contented ourselves with saying that it had been a favourable season for their eggs. The prodigious number of a sort of grub which did vast mischief about the same |